A picture of French tourist and mountain guide Herve Gourdel, 55, who was killed after being kidnapped on Sept. 21 while hiking in Algeria's Djurdjura National Park. The leader of the group that killed Gourdel has been killed in a military attack. Farouk Batiche/AFP/Getty Images hide caption

itoggle caption Farouk Batiche/AFP/Getty Images

The Islamist group Hamas, shown here in a rally in the Gaza Strip on Dec. 12, is the strongest faction in the Gaza Strip. The Islamic State, or ISIS, is not believed to be in the territory, though fliers purporting to be from the group have circulated in Gaza. They are widely believed to be fake, but both Israel and Hamas have tried to use them to their advantage. Mahmud Hams/AFP/Getty Images hide caption

itoggle caption Mahmud Hams/AFP/Getty Images

Many Yazidis, like the ones shown here, managed to flee the onslaught of the so-called Islamic State and made their way to relative safety, like this camp near the northern Iraqi border crossing of Zakho. However, some 5,000 Yazidis, many of them women, are still being held hostage by the Islamic State. EPA/Landov hide caption

itoggle caption EPA/Landov

A member of the Saudi border guards mans a machine gun at the border with Iraq in July. Since the so-called Islamic State launched its offensive this summer in Iraq, Saudi Arabia has sent thousands of troops to the region. Faisal Nasser/Reuters/Landov hide caption

itoggle caption Faisal Nasser/Reuters/Landov

Alfons R. of Hamburg, Germany (shown in this undated photo), converted to Islam at age 17. Later, he went to Turkey, then Syria, to join ISIS. He was killed this past summer. Courtesy of Manfred Karg hide caption

itoggle caption Courtesy of Manfred Karg

Secretary of State John Kerry, left, Iraqi Prime Minister Haider al-Abadi, center, and Iraqi Foreign Minister Ibrahim al-Jaafari prior to a round table meeting of the global coalition to counter the Islamic State. Virginia Mayo/AP hide caption

itoggle caption Virginia Mayo/AP

The Islamic Youth Council in Derna, in eastern Libya, is among the local militant groups from Egypt to Libya that have reportedly pledged allegiance to the self-proclaimed Islamic State. Reuters/Landov hide caption

itoggle caption Reuters/Landov

Iraqi Kurdish soldiers, or peshmerga, patrol an area in the recently recaptured town of Zumar, near Mosul in northern Iraq on Oct. 29. When the Islamic State captured the town in August, the Kurds fled. Now that the Kurds are in control, the Arabs are all gone. STR/EPA /LANDOV hide caption

itoggle caption STR/EPA /LANDOV

President Obama speaks to the media before meeting with his Cabinet in the White House Friday. The president is ordering up to 1,500 additional military personnel to Iraq, to help Iraqi and Kurdish forces fight the extremist group ISIS. Evan Vucci/AP hide caption

itoggle caption Evan Vucci/AP

Aza Betwata (left) and his brother Mirwan (center) left Holland to join the Kurdish peshmerga fighting against ISIS militants in northern Iraq. Though the brothers come from a family of fighters, Aza had just two days of training — his brother must show him how to strip and clean his rifle. Alice Fordham/NPR hide caption

itoggle caption Alice Fordham/NPR

A family passes through Maktab Khaled in northern Iraq, the last Kurdish checkpoint before they make their way to Kirkuk. ISIS-controlled territory lies less than a mile away. Leila Fadel/NPR hide caption

itoggle caption Leila Fadel/NPR

Alleged Islamic State militants stand next to an ISIS flag atop a hill in the Syrian town of Ain al-Arab, called Kobane by the Kurds, as seen from the Turkish-Syrian border in Suruc, Turkey, on Monday. Aris Messinis/AFP/Getty Images hide caption

itoggle caption Aris Messinis/AFP/Getty Images

"Today's anti-Westernism is a reaction to yesterday's racism," Iranian President Hassan Rouhani said in a speech at the U.N. General Assembly on Thursday. Jason DeCrow/AP hide caption

itoggle caption Jason DeCrow/AP

Fighters from the Islamic State group parade in their northern Syrian stronghold, Raqqa. Uncredited/AP/Raqqa Media Center hide caption

itoggle caption Uncredited/AP/Raqqa Media Center